We are indeed buying 2 carriers. However, we will only have enough manpower, money and escorts to normally have one at sea. The "surge" number of F-35Bs on the QEC is around 40 airframes - impossible organically with a fleet size of 48, but perfectly "do-able" if third party F-35B operators (USMC, Italy) contribute assets. IMHO a fleet of around 70 F-35B would be sensible to enable one "surge" CAG or even enough for both QECs to have TAGs in extremis. Re the nefarious Crabs, the Tornado needs replacing. Typhoon has replaced the F3/Jag and is swing-role capable of covering elements of the GR4 role, but the additional survivability conferred by the F-35's LO elements and SA make it better placed for many mission sets such as SEAD, EA and attacks against highly defended targets. For this role the F-35A or C are better as they can carry, internally, 2000lb class weapons and both have longer range than the "B" thanks to increased fuel and not carrying powered lift mechanisms with them. The decision between A and C comes down to picking between more "g", lower cost and internal gun (A) or probe/drogue refuelling (C). Pay yer money, makes yer choice. The 138 number is also, seemingly, viewed as a "lifetime buy" and may take decades to be fully delivered as the lines will be open for a long time. I'd even suggest that with fatigue/attrition we'll likely see more "tails" than 138 by OSD - aircraft like the Chinook in the RAF have benefited from long production runs with the opportunity to "dip in" when finances and needs dictate.